1. Field of the Invention
The present invention relates to a manufacturing system for producing a light emitting device that has an EL element on a substrate, specifically, a manufacturing system of a layer of a highly pure organic compound. The present invention also relates to a method of operating a manufacturing apparatus as well as a light emitting device obtained by the operation method. Also related to the present invention is an organic compound recycling system.
2. Description of the Related Art
The study of light emitting devices in which light emitting elements such as EL elements are used has become active in recent years. In particular, a light emitting device using EL material comprising an organic material is attracting attention. Such a light emitting device is called an EL display comprising an organic material or a light-emitting diode comprising an organic material.
Note that EL elements have a layer containing an organic compound in which luminescence develops by adding an electric field (electroluminescence) (hereinafter referred to as EL layer), an anode, and a cathode. There is light emission when returning to a ground state from a singlet excitation state (fluorescence), and light emission when returning to a ground state from a triplet excitation state (phosphorescence) in the organic compound luminescence, and it is possible to apply both types of light emission to light emitting devices manufactured by the film forming apparatus and film formation method of the present invention.
Unlike liquid crystal display devices, light emitting devices are of a self-luminous type, so there is no problem of a view angle. More specifically, a light emitting device is more suitable as a display used outside, compared with a liquid crystal display. Thus, the use of light emitting devices in various forms has been proposed.
Further, there are two systems for light emitting devices the first being an EL layer formed between two kinds of stripe-shaped electrodes provided so as to be orthogonal to each other (passive matrix system) and the second being an EL layer formed between pixel electrodes arranged in a matrix so as to be connected to a TFT and a counter electrode (active matrix system).
EL elements have a structure in which an EL layer is sandwiched between a pair of electrodes, and the EL layer normally has a laminate structure. Examples of laminate structures may include “hole transporting layer/light emitting layer/electron transporting layer”, which have extremely high light emitting efficiency.
Further, a structure in which: a hole injecting layer, a hole transporting layer, a light emitting layer, and an electron transporting layer are laminated in this order on an anode; or a hole injecting layer, a hole transporting layer, a light emitting layer, an electron transporting layer, and an electron injecting layer are laminated in this order on an anode may also be used. Fluorescent pigments and the like may also be doped into the light emitting layers. Further, all of the layers may be formed using low-molecular weight materials, or some of the layers may be formed using high-molecular weight materials.
Note that all layers formed between a cathode and an anode are referred to generically as EL layers in this specification. The aforementioned hole injecting layer, hole transporting layer, light emitting layer, electron transporting layer, and electron injecting layer are therefore all included in the category of EL layers.
Further, in this specification, the EL element is a light emitting element formed of a structure in which a layer including an EL material and an organic or inorganic material for introducing a carrier to the EL material (hereinafter referred to as an EL layer) is sandwiched between two electrodes (an anode and a cathode), and is a diode formed from an anode, a cathode, and the EL layer.
With an EL element using EL material comprising an organic material, a structure of an EL layer formed with a combination of EL material and organic material is commonly used. Although the EL material comprising organic material or organic material is generally classified into low-molecular weight (monomer based) material, and high-molecular weight (polymer based) material, the low-molecular weight material primarily forms a film with vapor disposition.
The most serious problem of practical use of these EL elements lies in that the element's life is insufficient. Degradation of an element is exhibited in such a manner that a non-light emitting region (dark spot) spreads along with light-emission for a long period of time, which is caused by the degradation of an EL layer.
EL material forming an EL layer is easily degraded by impurities such as oxygen and water. Furthermore, it is possible that inclusion of other impurities in EL materials may cause an EL layer to be degraded.
Major examples of a process that allows oxygen, water and other impurities to contaminate an EL material to be subjected to evaporation include a process of setting an EL material in an evaporation apparatus before evaporation and an evaporation process.
Usually, a container keeping an EL material is put in a brown glass jar and the jar is lidded with a plastic lid (cap). The airtightness of the container keeping an EL material may be insufficient.
In prior art, when a film is formed by evaporation, a given amount of evaporation material is taken out of its container (glass jar) and is moved into a container (typically, a melting pot or an evaporation boat) set opposed to an object on which the film is to be formed in the evaporation apparatus. The evaporation material could be contaminated by impurities during moving the evaporation material. To elaborate, oxygen, water, and other impurities that can cause degradation of an EL element could mix with the evaporation material.
One way to move an evaporation material from a glass jar to a container is by hand in a pretreatment chamber equipped with an evaporation apparatus having a glove box or the like. However, a pretreatment chamber equipped with a glove box does not allow vacuum and the work has to be done in atmospheric pressure. A nitrogen atmosphere can be employed but even then the amount of moisture and oxygen in the pretreatment chamber is not small enough. The use of a robot is possible but impractical since it is not easy to create a robot that can transfer evaporation material in a powder form between containers. This makes it difficult to build an integrated closed system in which steps from forming an EL layer on a lower electrode and till forming an upper electrode are automated to avoid impurity contamination.
Although a light emitting device maker could refine an evaporation material bought from a material maker to further enhance the purity of the evaporation material, refining is laborious and still presents a chance for impurity contamination when an evaporation material is set in an evaporation apparatus.
In addition, an EL material is very expensive and it costs more per gram than gold does per gram. It is therefore desired to use an EL material as efficiently as possible.